Surgical techniques for closing openings and repairing defects in anatomical lumens and tissues, such as blood vessels, septal defects and other types of physiological irregularities and defects, are highly invasive. Surgical methods for clipping aneurysms, for example, require opening the skull, cutting or removing overlying brain tissue, clipping and repairing the aneurysm from outside the blood vessel, and then reassembling tissue and closing the skull. Surgical techniques for repairing septal defects are also highly invasive. The risks associated with anesthesia, bleeding and infection during and following these types of procedure are high, and tissue that is affected during the procedure may or may not survive and continue functioning.
Minimally invasive surgical techniques may alternatively be used to place occlusive devices within or across an opening or cavity in the body, such as in the vasculature, spinal column, fallopian tubes, bile ducts, bronchial and other air passageways, and the like. In general, an implantable device is guided to a desired site through a delivery catheter and may be pushed through an opening at the distal end of the delivery catheter by a pusher mechanism, such as a pusher or delivery wire, thereby deploying the device at the desired site of intervention. Once the occlusive device has been placed at the desired location, it is detached from the pusher mechanism without disturbing placement of the occlusive device or damaging surrounding structures.
Aneurysms are bulges in an artery wall, generally caused by a weakening in the artery wall, that form an opening or cavity and are often the site of internal bleeding and stroke. In general, the minimally invasive therapeutic objective is to prevent material that collects or forms in the cavity from entering the bloodstream, and to prevent blood from entering and collecting in the aneurysm. This is often accomplished by introducing various materials and devices into the aneurysm.
Various types of embolic agents and devices are used to reduce risks to a patient associated with the presence of an aneurysm. One class of embolic agents includes injectable fluids or suspensions, such as microfibrillar collagen, various polymeric beads and polyvinylalcohol foam. These polymeric agents may be cross-linked (sometimes in vivo) to extend the persistence of the agent at the vascular site. These agents are often introduced into the vasculature through a catheter. After introduction and at the site, the introduced materials form a solid space-filling mass. Although some of these agents provide for excellent short term occlusion, many are thought to allow vessel recanalization due to absorption into the blood. Other materials, such as hog hair and suspensions of metal particles, have also been proposed and used to promote occlusion of aneurysms. Polymer resins, such as cyanoacrylates, are also employed as injectable vaso-occlusive materials. These resins are typically mixed with a radiopaque contrast material or are made radiopaque by the addition of a tantalum powder. Accurate and timely placement of these mixtures is crucial and very difficult. These materials are difficult or impossible to retrieve once they have been placed in the vasculature.
Implantable vaso-occlusive metallic structures are also well known and commonly used. Many vaso-occlusive devices are provided in the configuration of helical coils and are constructed from a shape memory material that forms a desired coil configuration upon exiting the distal end of a delivery catheter. The purpose of the coil is to fill the space formed by a defect or injury and facilitate formation of an embolus with the associated allied tissue. Multiple coils of the same or different structures may be implanted serially in a single aneurysm or other vessel defect during a procedure. Implantable framework structures are also used in an attempt to stabilize the wall of the aneurysm or defect prior to insertion of filling material such as coils.
Techniques for delivering a vaso-occlusive device to a target site generally involve a delivery catheter and a detachment mechanism that detaches the device, such as a coil, from a delivery mechanism after placement at the target sue. A microcatheter is initially steered through the delivery catheter into or adjacent to the entrance of an aneurysm, typically aided by the use of a steerable guidewire. The guidewire is then withdrawn from the microcatheter lumen and replaced by the implantable vaso-occlusive coil. The vaso-occlusive coil is advanced through and out of the microcatheter and thus deposited within the aneurysm or other vessel abnormality. Implantation of the vaso-occlusive device within the internal volume of a cavity and maintenance of the device within the internal volume of the aneurysm is crucial. Migration or projection of a vaso-occlusive device from the cavity may interfere with blood flow or nearby physiological structures and poses a serious health risk.
One type of aneurysm, commonly known as a “wide neck aneurysm” is known to present particular difficulty in the placement and retention of vaso-occlusive coils. Wide neck aneurysms are generally referred to as aneurysms of vessel walls having a neck or an entrance zone from the adjacent vessel that is large compared to the diameter of the aneurysm or that is clinically observed to be too wide to effectively retain vaso-occlusive coils deployed using the techniques discussed above.
The placement of coils, or other structures or materials, in the internal space of an aneurysm or other defect has not been entirely successful. The placement procedure may be arduous and lengthy, requiring the placement of multiple devices, such as coils, serially in the internal space of the aneurysm. Longer procedures, in general, involve higher risks of complication from anesthesia, bleeding, infection, and the like. Moreover, because placement of structures in the internal space of an aneurysm doesn't generally completely occlude the opening, recanalization of the original aneurysm is more likely to occur, debris and occlusive material may escape from within the aneurysm and present a risk of stroke, vessel blockage or other undesirable complications. Blood may also flow into aneurysm and other blood vessel irregularities after the placement of embolic devices, which increases the risks of complication and further enlargement of the aneurysm. Furthermore, some aneurysms, vessels and other passageway defects are not well-suited to placement of coils or other conventional occlusive devices.
Devices for maintaining vaso-occlusive coils within an aneurysm nave been proposed. One such device is described in U.S. Pat. No. 5,980,514, which discloses devices that are placed within the lumen of a feed vessel exterior to the aneurysm to retain coils within the aneurysm cavity. The device is held in place by means of radial pressure of the vessel wall. After the device is released and set in an appropriate place, a microcatheter is inserted into the lumen behind the retainer device and the distal end of the catheter is inserted into the aneurysm cavity for placement of one or more vaso-occlusive devices. The retainer device prevents migration of occlusive devices from the cavity. A removable occlusion system for covering the neck of an aneurysm while embolic material is delivered to the aneurysm is described in U.S. Pat. No. 5,928,260.
Another methodology for closing an aneurysm is described in U.S. Pat. No. 5,749,894, in which a vaso-occlusive device, such as a coil or braid, has on its outer surface a polymeric composition that reforms or solidifies in situ to provide a barrier. The polymer may be activated, e.g. by the application of light, to melt or otherwise to reform the polymer exterior to the vaso-occlusive device. The vaso-occlusive device then sticks to itself at its various sites of contact and forms a rigid whole mass within the aneurysm.
Devices for bridging the neck of an aneurysm have also been proposed. U.S. Patent Application Publication No. 2003/0171739 A1, for example, discloses a neck bridge having one or more array elements attached to a junction region and a cover attached to the junction region and/or the array elements. The array elements may comprise Nitinol alloy loops and the cover may comprise a fabric, mesh or other sheeting structure.
U.S. Patent Application Publication No. 2004/0087998 A1 discloses a device and method for treatment of a vascular defect in which two sheets, or a sheet and a strut structure function to secure the vaso-occlusive device and to occlude an opening. This patent publication lists numerous biocompatible compositions and materials that may be used in connection with the device to promote adhesion, fibrosis, tissue growth, endothelialization or cell growth.
U.S. Patent Application Publication No. 2004/0193206 A1 discloses another device for at least partially occluding an aneurysm including a plurality of elongate members configured to move relative to one another to transform the bridge between the delivery and deployed configurations. A two array bridge, in which a first array is deployed inside the aneurysm and a second array is deployed outside the aneurysm is also disclosed.
U.S. Patent Application Publication Nos. 2007/0088387 A1 and 2007/01918844 A1 disclose methods and systems for repairing defects in physiological lumens, such as aneurysms by placing occlusive devices having closure structures covering the opening, when deployed, and anchoring structures contacting the inner aneurysm wall, or the parent vessel, or both.
Septal defect closure devices are also well known. Such devices occlude openings, or septal defects, in the heart or the vascular system. Septal closure devices are disclosed, for example, in U.S. Pat. Nos. 6,077,291 and 6,911,037. Bronchial flow control devices that seal or partially seal a bronchial lumen are also known, see, e.g., U.S. Pat. No. 7,011,094.
Systems currently used for the detachment of implantable devices after placement include mechanical systems, electrolytic systems and hydraulic systems. In mechanical systems, the occlusive device and the pusher wire are linked by means of a mechanical joint, or inter-locking linkage, which separates once the device exits the delivery catheter, thereby releasing the device. Examples of mechanical systems include those taught in U.S. Pat. Nos. 5,263,964, 5,304,195, 5,350,397, and 5,261,916. In electrolytic systems, a constructed joint (generally either fiber- or glue-based) connects the pusher wire to the occlusive device and, once the device has been placed in the desired position, the joint is electrolytically disintegrated by the application of a current or heat. An example of an electrolytic system is provided in U.S. Pat. No. 5,624,449. In hydraulic systems, the pushing wire is connected to the occlusive device by means of a polymer coupling. The pushing wire contains a micro-lumen to which the physician attaches a hydraulic syringe and, upon the application of pressure using the syringe plunger, the hydraulic pressure forces the polymer joint to swell and break, thereby releasing the device. An example of a hydraulic system is described in U.S. Pat. No. 6,689,141.
Despite the numerous devices and systems available for placing embolic materials in an aneurysm and for occluding physiological defects using minimally invasive techniques, these procedures remain risky and the results rarely restore the physiological structure to its normal, healthy condition. Challenges also remain in accurate positioning of implantable devices during deployment, preventing shifting or migration of implantable devices following deployment, and preserving flow in neighboring vessels following placement of implantable devices. Methods and systems of the present invention are directed, among other things, to reducing the length and complexity of minimally invasive procedures for supporting and occluding openings and repairing a lumen or tissue defect, and to restoring a physiological structure, such as a blood vessel, to its normal, healthy condition. Methods and systems of the present invention are additionally directed to providing implantable devices for supporting and/or at least partially occluding an opening or cavity, such as an aneurysm, that are safely and conveniently deployable using minimally invasive techniques, that reduce shifting and migration following placement, and that do not restrict blood flow in neighboring vessels following deployment.